Field of the Invention
The present invention relates to a display device and a method of driving the same, and more particularly, to an organic light emitting device and a method of driving the same.
Background of the Invention
A pixel of an organic light emitting device includes an organic light emitting element and a thin film transistor (TFT) that drives the same.
The TFT is classified into a polysilicon TFT and an amorphous silicon TFT according to the kind of an active layer. An organic light emitting device using a polysilicon TFT may have high electron mobility, good high frequency operation characteristics, and a low leakage current. However, it may not be easy to uniformly form characteristics of a semiconductor that is included in a TFT within a display device in a process of manufacturing an active layer with polysilicon. That is, a threshold voltage or mobility of the TFT may be different in each transistor. Accordingly, a luminance deviation may occur between a plurality of pixels that are included in the display device.
As a current flows for a long time period, a threshold voltage of the organic light emitting element may vary. In a p-channel TFT, because the organic light emitting element is positioned at a drain side of the TFT, if a threshold voltage of the organic light emitting element is degraded, a voltage of the drain side of the TFT may be changed. Accordingly, even if the same data voltage is applied to a gate of the TFT, a voltage between a gate and a drain of the TFT may be changed, and thus a non-uniform current may flow to the organic light emitting element. A non-uniform current flow may be a factor of degradation of picture quality of the organic light emitting device.
A hold type of flat panel display device such as an organic light emitting device displays a fixed image for a predetermined time period, for example for one frame, regardless of whether a still picture or a motion picture is shown. For example, when displaying an object that continuously moves, the object may stay at a specific position for one frame and may stay at a position to which the object moves after a time period of one frame in a next frame. Thus, a motion of the object may be discretely displayed. Because a time period of one frame is a time period in which an afterimage is sustained, even if a motion of the object is displayed in this way, a motion of the object may be continuously viewed.
However, when viewing a continuously moving object through a screen, because a line of sight of a person continuously moves along a motion of the object, the line of sight of a person may collide with a discrete display method of the display device and thus a blurring phenomenon of a screen may occur. For example, it is assumed that the display device displays images as an object stays at a position A in a first frame and at a position B in a second frame. In the first frame, a line of sight of a person moves from the position A to the position B along an estimated movement path of the object. However, the object is not actually displayed at an intermediate position, just at the positions A and B.
Finally, because luminance that is recognized by a person for the first frame is an integrated value of luminance of pixels in a path between the position A and the position B, i.e., an average value between luminance of an object and luminance of a background, an object may be blurredly viewed.
Because a degree in which an object is blurredly viewed in a hold type of display device may be proportional to a time period in which the display device sustains the display, a so-called impulse driving method in which an image is displayed for only a partial time period within one frame and a black color is displayed for the remaining time period may be used.